The invention relates to an inhaler for introducing a metered amount of solids into a stream of air drawn in by a user.
Solids inhalers are nowadays obtainable in large numbers and in many different designs. These inhalers are used principally for inhaling pharmaceutically active substances or mixtures of substances, especially powdered substances or mixtures of substances. Such an inhaler is known, for example, from CH-A-666,823. The inhaler described therein comprises a storage chamber for the solids as well as an air channel which connects an air inlet opening for the air drawn in with an outlet for the solids/air mixture produced in the inhaler. For fixing the amount of solids and for introducing that fixed amount of solids into the air stream there is a metering rod which is provided with a metering recess and which is constructed to be rotatable about its longitudinal axis. In a first position, the metering recess of the metering rod picks up the amount of solids fixed by the volume of the metering recess. Then the metering rod is rotated through 180.degree. about its axis into a second position in which the solids are able to fall out of the metering recess and thus pass into the air channel, where they are mixed with the stream of air.
the inhaler described has various disadvantages. For example, the solids must be readily flowable in order to ensure that the metering recess is always filled quickly, reliably and completely. However, since granules and other relatively coarse solids are unsuitable for inhalation, the pharmaceutically active substances or mixtures of substances, for example anti-asthmatically active substances or mixtures of substances, are frequently in the form of a very small-grained powder. However, these small-grained powders generally have the very disadvantageous property of not being flowable or of being only very poorly flowable. This in turn may result in incomplete filling of the metering recess and thus in variations in the metered amount of solids. A user who is having difficulty in breathing (for example as a result of an asthma attack) must, however, be able to inhale a specific amount of powder quickly and reliably in order to obtain rapid relief.
A further disadvantage of the described inhaler is that the solids are introduced into the air channel by means of a rotatable metering rod. Solids may therefore get into the hollow spaces (bearing) around the rotatable metering rod, with the result that the metering rod can be rotated only with very great difficulty or even "siezes up" completely, which can have serious consequences especially for users prone to asthma, since the device may not be in good working order in an emergency.
A further disadvantage of the described inhaler is the fact that the small-grained powders in the storage chamber cannot be stored in a separate storage container, for example a capsule. This is especially disadvantageous for powders whose pharmaceutical activity decreases when they are stored in permanent contact with the air. Moreover, with the above-described inhaler, moisture entering the inhaler and its storage chamber (for example as a result of the user accidentally coughing into the inhaler) may cause further impairment of the flow properties of the powder, which in most cases are already poor, or may cause lumps to form.